Grinding and classifying device



June 2 1942. c. H. KIDWELL 2,284,746

GRINDING AND CLASSIFYING DEVICE Filed March 4, 1939 INVENTOR. (Z00fluvldliidwell r Patented June 2; 1942 UNITED STATES PATENT OFFICEGRINDING AND CLASSIFYING DEVICE Cleo Harold Kidwell, Short Hills, N. If

Application March 4, 1939, Serial No. 259,819

8 Claims.

The present invention relates to apparatus for reducing or grindingmaterials, and more particularly to an improved form of grindingapparatus whereby a greater uniformity of particle size in the finishedproduct is attainable.

The development of this art has been in the main concerned withimprovements in methods of reducing over-sized and irregularly sizedmaterials in grinding mills, and to this end it has been discovered thatparticles of material to be treated may be suspended in a carrying fluidmedium and introduced into a reducing mill hav-.-

ing a substantially curved tubular grinding sized particles areseparated from the final product.

I have discovered that this objectionable condition whereby over-sizedparticles are carried over into the final product may be avoided bymeans of a certain definite mill structure in which the discharge oroutlet from the mill is located on the inner periphery of a curvedportion of the tube. This result obtains from the fact that the doublehelical flow effect produced in the above described grinding devicesresults in the tendency of the moving material to remain in the outerportions (radially speaking) of the described curved tubular grindingchamber.

Hence by locating means for removing the treatedv material from the millon the inner periphery of the curved portion, a product is achieved,characterized by a controlled maximum particle size substantially finerthan heretofore available.

An object of the invention, accordingly, is to provide an improved formof grinding device whereby a product is attained which is characterizedby controlled uniformity of particle size substantially flner than hasbeen heretofore available.

A further object of the invention is to provide a grinding device whichmay be kept in continual operation, simultaneously introducing untreatedmaterial into the grinding chamber and withdrawing that portion of thematerial which has been reduced to the desired particle size.

A further object of the invention is to provide a grinding mill formedto produce. the double helical flow, and constructed so that thecharacteristics of the flow are utilized to facilitate removal of thereduced particles from the grinding chamber.

Further objects of the invention will be apparent as it is described indetail with the accompanying drawing, wherein:

Figure 1 is a side view of one form of the grinding device;

Figure 2 is a modification thereof wherein the device has a helicalform; and

Figure 3 is a view in front elevation showing a modification of thedevice that is of oval form.

Referring to the above drawing, and particularly to the modification ofthis invention shown in Figure 1, a U-shaped tube H] of substantiallycircular cross-section is provided with an axially disposed inletconduit l3 secured on one end thereof, and an outlet pipe l4 leading toa suitable exhaust chamber. A material suspending fluid under pressureis introduced through the inlet conduit l3 by means of a nozzle l5 whichis carried by the conduit l3. The suspending fluid is introduced intothe grinding chamber ll of the mill I!) through nozzle l5 by a supply.

pipe 16, the directional flow of the fluid stream being as indicated bythe arrow in Figure 1.

The material to be reduced is introduced into the fluid stream by meansof a nozzle H, which is provided with a chamber l8 formed in conduit l3immediately in advance of the nozzle I 5. A hopper l9 communicates withchamber l8 and thus supplies material to the jet issuing from nozzlel'l, entraining the material in the fluid stream and directing it intonozzle IS. The material suspended in the fluid stream is directed intothe grinding chamber II at a pressure greater than that in the saidchamber, whereupon the fluid stream flOWs through the chamber under theflow conditions described above.

It will be observed that since the centrifugal force of the heavierparticles is greater than that of the smaller or more reduced particlesthe tendency of the larger particles to be entrained in the entrainingmedium will be less pronounced than that of the smaller particles andthe former will tend to remain adjacent the outer wall of the curvedtube. As the larger particles are reduced by attrition, they willgradually become more subject to the characteristic flow of thesuspending fluid by reason ofits viscosity. When the particle size hasbeen sufliciently reduced the effect of centrifugal force is overcomesufliciently to permit entrainment of the particles in the fluid streamto such extent that the double helical flow of the fluid streamexercises a selective control thereover, carrying the entrainedparticles to a point adjacent the inner portion of the tubular chamberwall, the larger particles remaining in the outer portion of the tube.It will thus be observed that the characteristic flow of the suspendingfluid in the curved tubular portion of the mill is utilized as a meansof selecting the finely reduced particles from the mass, carrying themto the inner periphery of the grinding chamber during operation of themill.

Advantage is taken of this condition to improve the uniformity ofcollection by providing an outlet pipe 20 at the inner periphery of thecurved tubular wall for removing the said particles, said )utlet pipe 20communicating with a suitable col- .ecting device. Insufiicientlyreduced particles in ;he curved grinding chamber are maintained awayfrom the outlet 20 by centrifugal force and are discharged with thesuspending fluid through outlet pipe 14, where they may be collected inany suitable collecting device for subsequent reproc essing, if desired.

In one preferred embodiment of the invention, outlet 20 is located onthe inner periphery of the curve and lies at an angle to the axis of thetube and in a direction generally reverse to the direction of flowthrough the tube. This formation further avoids collection of over-sizedparticles.'

In the structure shown in Figure 2, the present invention is embodied inan annular ring formation, the material to be reduced being introducedinto the annular ring 22 thereof by means of a nozzle 2| which may besimilar to the corresponding element of the structure described inFigure 1. An annular grinding chamber 22a is provided with an outlet 23positioned on the inner wall of the grinding chamber at a point remotelysituated from inlet pipe 2|, in the direction of the fluid flow, thusfully utilizing the reducing effect of the double helical flow producedin the mill chamber before exhausting the concentration of reducedparticles from the inner wall thereof. As described in connection withthe embodiment of the invention shown in Figure 1, outlet 23 ispreferably angularly disposed in relation to the inner wall of thechamber in the opposite direction to that of the fluid flow, thusavoiding undesirable collection of insufficiently reduced particles andaccumulations of reduced particles therein.

It will be noted that as the centrifugal force of the larger particlesis greater than that of the reduced particles, the former tend to remainnear the outer periphery of the curved section 22 of the mill, and thusescape discharge until sufliciently reduced to be entrained in thedouble helical flow of the suspending medium. Those particles which areunreduced during their first revolution through the grinding chamberremain in the device, being carried over for further treatment untilsufliciently reduced to be entrained in the fluid flow.

In the structure shown in Figure 3, the reducing mechanism is shown asassuming an elliptical form, consisting of a straight entrance tube 24which may be supplied with material to be reduced through a hopper 25,the material entraining means being otherwise similar in contsruction tothe corresponding elements shown in Figures 1 and 2. The straightsection 24 communicates with curved end section 26 which in turnconnects with a straight section 21 and curved end section 28. Thelatter communicates with straight section 24 through straight section29. Reduced particles are exhausted from the mill through outlet pipe 3|located on the inner wall of curved section 28, being positionedremotely from the inlet pipe 24 in the direction of the fluid flow, soas to fully utilize the reducing action of the characteristic flowproduced in the curved tubular portion of the device before exhaustingthe ma terial from the mill. Outlet 3| is disposed at an acute angle inrelation to the inner wall of section 28 in a direction opposite to thatof the fluid flow, in a manner similar to the outlet structures shown inFigures 1 and 2. In operation it is preferred that this mill besupported so that it lies in a vertical plane.

It will thus be seen that the present invention provides an effectivemeans of increasing the efiiciency of grinding mechanisms utilizing achar acteristic double helical flow as a means of reducing the particlesby attrition. The present invention also provides means allowingcontinued operation of such grinding apparatus, with simultaneousintroduction of untreated material into the grinding chamber andwithdrawal of the reduced product being possible. Furthermore, byexhausting the reduced particles at a. point adjacent the innerperiphery of the curved tubular grinding chamber, the accumulation ofreduced material thereon is utilized with a resulting uniformity ofproduct heretofore unachieved in the art.

While the present invention has been described with reference tospecific structural elements of this invention, it is obvious that suchdetails are included only for purposes of illustration and that thescope of the invention is not to be limited save as defined in theappended claims.

I claim:

1. In apparatus for reducing material, the combination of a tube ofsubstantially circular cross-section having at least one curved'portiontherein and a total curvature of at least 180, means for supplying fluidto the tube for entraining and conveying material therein, and dischargemeans positioned substantially on the inner curved portion of the tubeand extending angularly therefrom in a direction opposite that of thefluid flow, for exhausting reduced material therefrom.

2. In apparatus for reducing material, the combination of a tube ofsubstantially circular crosssection having at least one curved'portiontherein and a total curvature of at least 180, means for supplying afluid to the tube for entraining and conveying material therein, anddischarge means on the inner curved portion of the tube, positioned atless than a angle to the axial tangent of the tube and extending in adirection reverse to that of the fluid flow, for exhausting reducedmaterial therefrom.

3. In apparatus for reducing material, the combination of a tube ofsubstantially circular crosssection having at least one curved portiontherein and a total curvature of at least means for supplying a fluid tothe tube for entraining and conveying material therein, and dischargemeans on the inner curved portion of the tube, positioned at less than a90 angle to the axial tangent of the tube and extending in a directionreverse to that of the fluid flow, being positioned remotely of the saidmeans in the direction of the fluid flow, for continually removingreduced material from the, inner periphery of the said tube.

4. In apparatus for reducing material, the combination of an endlesselongated tube of substantially circular cross-section being disposedabout a common axis to form a substantially closed circuit, means forsupplying a fluid to the tube for entraining and conveying the materialtherein, and discharge means positioned substantially on the inner wallof the tube and extending angularly therefrom in a direction reverse tothat of the fluid flow, being positioned remotely of the said means inthe direction of the fluid flow, for exhausting reduced materialtherefrom.

5. In apparatus for reducing material, the combination of an endlesselongated tube of substantially circular cross-section being disposedabout a common axis to form a substantially closed circuit, means forsupplying a fluid to the tube for entraining and conveying materialtherein, and discharge means positioned on the inner curved portion ofthe tube at less than a 90 angle to the axial tangent of the tube andextending in a direction reverse to that of the fluid flow, forcontinually removing reduced material from the inner periphery of thesaid tube.

6. In apparatus for reducing material, the combination of an endlesstube of substantially circular cross-section having a number of curvedportions in the length thereof, the said curved portions being connectedto form a substantially closed circuit, means for supplying a fluid tothe tube for entraining and conveying material therein, and dischargemeans positioned substantially on the inner wall of one of the saidcurved portions and extending angularly therefrom in a direction reverseto that of the fluid flow for exhausting reduced material therefrom.

7. In apparatus for reducing material, the combination of an endlesstube of substantially circular cross-section having at least two curvedportions in the length thereof, the said curved portions being connectedby substantially straight portions to form a closed circuit, means forsupplying a fluid to the tube for entraining and conveying materialtherein, and discharge means positioned substantially on the inner wallof one of the said curved portions remote in the direction of flow ofthe fluid from said means for supplying fluid and extending angularlytherefrom in a direction reverse to that of the fluid flow, wherebyreduced material is continually exhausted from the apparatus.

8. In apparatus for reducing material, the combination of an endlesstube of substantially circular cross-section having at least two curvedportions in the length thereof, the said curved portions being connectedby substantially straight portions to form a closed'circuit, means forsupplying a fluid to the tube for entraining and conveying the materialtherein, and discharge means positioned substantially on the inner wallof one of the said curved portions and being at less than a angle to theaxial tangent of the said curved portion of the tube and extending in adirection reverse to that of the fluid flow, whereby reduced material iscontinually exhausted from the apparatus.

CLEO HAROLD KIDVELL.

